Electric heat-control apparatus



J. S. DUNN BLBCTR'LU HEAT GONTROL APPARATUS.

Filed Jan. 3, 1929 Jly 15, 1930.

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Patented July 1s, 1930 1,770,481

UNITED STATES PATENT OFFICE JOHN BTBUTHERS DUNN, F PHILADELPHIA, PENNSYLVANIA ELECTRIC HEAT-CONTROL APPARATUS Application led January 3, 1929. Serial No. 330,120.

My invention relates to electric heat con` mercury should be the same for a given degree trol apparatus, and more particularly to a of inclination of the switch envelope.- Also, thermostatically controlled switch for vconinitial leveling is difficult and the pigtail coritrolling supply of current to electric heaterv nections often break or short circuit. In ad- 5 elements. dition to erratic or unreliable control, with 55 My invention resides in controlling means respect to the close temperature limits defor electric heater circuits comprising a thersired, a. mercury switch has a further disad` mostatic element and a circuit controller vantage, ;in that itis liable to fail altoadapted to be actuated thereby, said circuit gether after continued use to open or close controller having a resilient supporting arm the relay circuit controlling supply of cur- 60 for the movable contact and said arm having rent to the heater elements. It has been such characteristics that movement of said found that mercury switches in actual praccontact to full open or closed positions is eftice often fail entirely, due to chemical acfected in part by the arm itself and by a relation within the switch envelope or otherl tively small degree of movement of its actureasons, after several months of service in 65 ating means. connection with electric ranges, for example.

My invention resides in a system and appa- Whatever the cause of these failures, the ratus of the character hereinafter described fact remains that mercury switches have and claimed. proven inadequate and unreliable for attain- It has been prior practice to control the ing constant temperature regulations for va-A 70 circuits of electric heaters by a relay in turn riations of two to five degrees F. and concontrolled by a thermostatically actuated tinuing constant and accurate regulation for mercury switch. The usual type of mercury indefinite periods of time. switch comprises an envelope of insulating To overcome these disadvantages,Iprovide material as glass, having a pair of contacts sensitive circuit controlling means which is 75 extending through and spaced Within the en` actuated by relatively small degree of movevelope, and a body of mercury movable Withment of the thermostatic element, the contacts in the envelope and adapted to bridve said of the circuit controlling means being praccontacts. The use of a mercury swltch in tically indestructible at the normal relay this connection, however, has proved to be actuating currents usually employed. 80 disadvantageous in several important re- For an understanding of my invention refspects.. For example, where a close regulaence is to be had to the accompanying drawtion of the temperature limits is desired, it in in which: has been found that the mercury switch is Fig. 1 is a longitudinal sectional'view of a too insensitive to obtain such regulation. thermostatically actuated circuit controller. This may in part be due to the fact that as a Fig. 2 is a sectional plan view taken along mercury switch is used over an appreciable the line 2-2 of Fig. 1. length of time, certain chemical reactions Fig. 3 is a view similar to Fig. 2, showing within the switch envelope take place due to the circuit controller in closed position.

4 the arcing across the contacts, thereby form- Fig. 4 is a detailed view of the circuit 90 ing substances which tend to make the movecontroller.

Q ment of the mercury body more sluggish. Fig. 5 'is a diagrammatic View of a heater Accordingly when the thermostatic element control system. moves through a range representative of a Referring to Fig. 1, a cylindrical casing 4 predetermined variation in temperature, the or housing 1 has secured at one end thereof operation of the mercury switch is apt to be a tubular member 2 within which is rotatably uncertain, since its time of operation depends mounted a hollow shaft 3. Shaft 3 1s deentirely upon the mobility of the mercury signed so as to have a relatively small hearbody within the switch envelope, it being aping surface upon its supporting tube or bearparent thatthe mobility or activeness of the ing 2, and to this end has mounted thereon 09 collars 4 converging to relatively small bearing portions. Collars 5 and 6 are also mounted upon shaft 3 at the opposite ends thereof. A thermostatic element 7, which may be a bi-metallic strip in helical form, has one end secured to a shoulder 8 of collar 6, as by a screw 9, and the other end secured to the free end of rod 10 which is freely rotatable within hollow shaft 3. A cylindrical protecting casing 11 open at its outer end is mounted upon the end of the tube 2, as by threaded engagement, to protect the thermostatic element from mechanical injury.

Housing 1 comprises a base member 12 having mounted thereon, as by stud 13, 4a switch casing 14 which will be presently described. Base 12 has a circular opening 15 centrally thereof through which tube 2 eX- tends. A cap member 16 having a top portion 17 ts over the outer walls of housing 1, and is rotatable with respect thereto. A circular metallic strip 18, which is graduated to indicate different temperatures is secured to the outer surface of cap 16 and co-operates with a pointer 19 rigidly mounted upon base 12. n

Within cap 16 and upon the inner side of top 17 is mounted a stationary cam element 20, which upon rotation of cap 16 is adapted to co-act with adjusting means for determining the relative position of the thermostatic element with respect to the circuit controlling means.

To this end, the actuating surface of cam 20 is adapted to engage lug 21 carried b arm 22 which is mounted on rotatable sha t 24, which also carries arm 25. Arms 22 and 25 being rigidly mounted with respect to each other, are normally urged toward stop pin 27"1l and the cam actuating surface of cam 20 by a spring 23 surrounding shaft 24 co-acting with casing 1. Arm 25 has mounted thereon a lug 26 which bears between opposing portions 27 of a bifurcated member which comprises an extension of disc 28. Disc 28 has an o ening centrally thereof through which ro 10 and shaft 3 extend, and is connected frictionally, as by an adjusting screw 29, to a collar 30 mounted upon shaft 3.

Rotation of cap 16 therefore, and consequently cam 20, will cause rotation of disc 28 and shaft 3. which is in frictional engagement therewith, to move thermostatic element 7 with respect to rod 10.

Rod 10 extends through and beyond collar 30, being freely rotatable within the same, and has secured at its outer end within casing 1 a cam element 31having an actuating surface 32.

Referring more particularly to Figs. 2 and 3, cam 31 is shown 'in co-operating relation withv a resilient arm 32 secured at 33 to a casing 34. Casing 34 forms with switch mounting 14 a cover or enclosing structure for switch contacts 35 and 36. Contact 36 is fixed with respect to mounting 14 and is electrically connected, as by conductor 37, to binding post 38, which in turn is electrically connected by a conductor, not shown, to terminal 39. Movable contact 35 is carried by a resilient strip 40 of conducting material which is secured at one end, as by screws 41, to mounting 14. A conducting member 42 electrically connects strip 40 with a binding screw 43 connected by conductor 44 to terminal 45. Resilient vstrip 40 is formed so that it normally tends to assume a curvilinear or nonplanar shape, and to take the position shown in Fig. 3, in which the contacts are in the fully closed position. An adjustable abutment 46 which may be moved with respect to strip 4() by rotation of screw 47, serves as a fulcrum about which str/ip 4,() may be flexed. A pin 48 freely movable within cover 34 transmits pressure to strip 40 between abutment 46 and screw 41 in response to movement of cam actuated arm 32.

Referring particularly to Fig. 3. cam 31 is shown engaging arm 32 and exerting a cer` tain amount of pressure upon strip 40 through pin 48. Further rotation of cam 31 through a relatively small angle will cause sufficient pressure to bear upon strip 40 as to cause contact 35 to suddenly rotate about abutment 46, and to move away from fixed contact 36 andagainst a stop member 50 with a snap action. In other words the relatively small movement of pin 48 causes sufficient distortion of the strip 40 between abut-ment 46 and screw 41 to cause strip 40 to move from its normal curvilinear shape, beyond its neutral plane, and into a position where it takes a shape of reverse curvature, as compared with its normal curvature. This action in itself is well known, and forms the principle upon which various types of snap switches are designed.

As long as pin 48 exerts suicient pressure, whlch is comparatively slight, upon strip 40, the contacts will remain in the fully open position as indicated in Fig. 2, but upon release of pressure due to rotation of cam 31 in such direction that arm 32 moves away from- .cover 34, strip 40`through its inherent resiliency will snap back to the pos1t1on shownin Fig. 3 and will remain in .such position until cam 31 moves again to its predetermined actuating position.

A detailed illustration of the switch is shown in Fig. 4. Movable contact 35 is carried by the bifurcated strip 40, there being a V-shaped slot 51 having at its apex a hole 52 of small diameter formed in strip 40. The edges of hole 52 form a bearing surface for the pin 48, which is of larger diameter, the position of hole 52 bearing a predetermined relation to abutment 46 and mounting 41 for a given degree of sensitiveness of the switch.

scale 18.

Adjustment of the thermostatic element at its initial position is accomplished by loosening screw 29 land movin member 28 relative to collar which is in xed relation to shaft 3. Movement of member 28 also effects movement of arm 25, and consequently, the positioning of lug 21 with respect to cam 20. When the initial adjustment of the thermostat has been determined, depending on the range of temperatures to be encountered, screw 29 is tightened so that members 28and 30 move as one member. The temperature at which the circuit breaker is to be actuated is determined by rotation of cap 16 through its cover 17 to a position where the pointer 19 indicates the desired temperature upon Rotation of cap 16 causes cam 20, which is securedl integrally thereto, and which ofcourse is in cooperative relation with respect to scale 18, to en age through its actuating face the lug 21, t ereby rotating arms 22 land 25 about shaft 24 and moving member 28 by means of lug 26.

Since there is now a positive connection between the temperature adjusting cam 20 and shaft 3, shaft 3 Will be rotated in accordance with rotation of cam 20, and will accordingly produce torsional stresses in the helical thermostatic element 7, which stresses are relieved by imparting a certain degree of rotation to the free end of rod 10 to which the opposite end of the thermostatic element is attached. Rod 10, being freely rotatable Within shaft 3, is accordingl moved through an angle dependent upon t 1e degree of movement of caml 20, and consequently the cam actuating face of cam 31 is rotated with respect to arm 32 so that either a greater or a lesser degree of rotation than heretofore is required for the Cam to engage 'said arm, and consequently -to actuate the circuit breaker.

Fig. 5 shows diagrammatically a current supp y system for electric heater elements 53 and 54 connected through conductors 55 and 56 to a source of current E. A switch 57 is adapted to connect either one resistant or both of them in series across the source for generating differentdegrees of heat.' A circuit breaker 58 is adapted to make or break connections to the heater elements from the source of supply, and the switch is actuated by electro-magnetic means 59 in turn energized through a battery or other source of power 60 and a thermostat-ically controlled circuit breaker indicated by contacts 35 and 36 of the character above described.

The operation of the system shown in Fig. 5 is apparent, and it need only be stated that when the thermostatic element is in the position re resentative of a lower degree of heat than t at desired, contact 35 is in engagement with contact 36, thereby energizin a relay coil 59 and closing switch 58 so t at current may How through the heater elements. WVhen the temperature lof the elements reaches apredetermined high value, Contact 35 through its thermostatic actuator moves to open positionv as shown, and the coil 59 is deenergized and the circuit opened.

I have found that due to the sensitiveness of the circuit breaker a very close adjustment for temperature variation may be provided for, and as a matter of fact control within temperature variations of but two degrees to five degrees F. is possible with my invention. Furthermore, since the contact members may be made ofany suitable conducting material to resist the effects of arcing, land particularly since the arcing itself is greatly minimized due to the rapid snap action of the switch, the life of the circuit breaker will be practically indenite, and there will be no necessity of frequent replacements, as is necessitated by the use of mercury switches. Furthermore the circuit breaker will always act at the same pressure, Was exerted by pin 48, and there will be no erratic action of the switch contacts as is generally the case with mercury switches after a certain amount of use.

It will b'e understood that a reasonable degree of departure may be made from the construction above described without departing from the spirit of my invention, and particularly with respect to the thermostatic actuating means for the Circuit controller.

What I claim is:

1. In control apparatus of the character described, a support, a thermostatic element movable in res )onse to varying degrees of heat to which tie same may be subjected, a member rotatable by said element, switch operating means engaged by said member in different positions thereof, a switch mounting secured to said support, stationary and movable contacts secured to said mounting, said movable contact carried by a resilient member normally curvilinear in form, and means interconnecting said operating means and last-named member whereby a relatively small degree of inovementof said thermostatic element'changes the curvilinear form of'said member to initiate movement thereof and effect either fully open or closed positions of the switch.

2. In control apparatus of the character described, a support, a thermostatic element movable in response to varying degrees of heat to which the same may be sub]ected, a member rotatable by said element, switch operating means yieldingly engaged by said member in different positions thereof whereby independent movement of saitl member with res ect tov said operating means is permitte a switch vsecured to said supportcomprising fixed and movable contacts, said movable contact carried by a flexible strip tending to normally assume a curvilinear form and having such characteristics that movement of said contact to fullyopen or by movement of the closed position is eected by initial movement of said operatinv means and thereafter exible strip itself into or out of its normal form'.

3. In control apparatus of lthe character described, a support, adjusting means rotatable within said support, a thermostatic element secured to said means and to a member rotated thereby, a cam mounted on said member for yieldingly engaging a switch actuator, a switch casing mounted upon said support and enclosing contact members, one of said contact members carried by a flexible strip tendingr normally to assume a nonplanar form, and means for transmitting movement from said actuator to said strip whereby initial movement of said strip is effected, the completed movement being effected by the inherent resiliency of the strip itself.

4. Apparatus for controlling supply of current comprising a thermostatic element movable in accordance with temperature conditions to which the same may be subjected, a cam member actuated thereby, an operating arm coacting With said cam member, and a relatively sensitive switch member of the snap-over type adapted to be moved to either fully open or closed position by relatively small degree of movement of said cam member.

5. Apparatus for controlling supply of current comprising a thermostatic element movable in accordance with temperature conditions to which the same may be subjected, a cam member rotatable by said thermostatic element, a resilient operating arm coacting with said cam element, a support for fixed and movable contacts, said movable contact carried by a resilient member normally tending to assume a non-planar shape, and means interposed between said operating arm and resilient member for transmitting pressure thereto causing change in its shape to initiate movement thereof whereby said movable contact continues to move by snap action either into or out of engagement with said fixed contact'.

JOHN STRUTHERS DUNN. 

